Digital illustrators use programs that are based on
raster or vector interpretation of data, and all of us who have worked with
Adobe Photoshop and Adobe Illustrator have experienced how different the
workings of the two programs can be. Illustrator tends to be used more by
illustrators and graphic designers that tend to focus more on object making. Illustrator
is referred to as “object oriented” software. Photoshop tends to be used more
by illustrators, photographers and designers who lean more toward making
pictures. Of course these assumptions are not absolute, and the developers of
both Illustrator and Photoshop have blurred the lines between raster and vector
as they have evolved. This comes from each program attempting to provide a
totally functional software solution. For instance, Illustrator uses some
raster display effects and offers the user an option to rasterize elements and
to use raster painting effects. Alternatively, Photoshop offers Bezier pen tool
functionality, the option to use vector masks, and to create and save outlines. So with the cross
adaptation between raster and vector, these software programs offer
illustrators new options that didn’t exist a few years ago. And on top of all
this, software programs like InDesign allow the use of both raster and vector components
in a single document. One thing that can help illustrators and graphic
designers make the decision as to which direction to go is to consider the
purpose for the illustration, i.e., the software choice is determined by how
the image must function. In order to make that decision an understanding of
properties of raster and vector imaging is indispensable.
Vector
Vector software is object oriented, a collection of
objects that always retain their integrity. Straight and curved lines, gradients,
and shapes including letterforms are an expression of mathematical descriptions.
The positions, scale, and display attributes of all objects are noted
mathematically using algebraic equations. Altering objects within an image
results in an alteration of the mathematical data. This form of image
processing preserves the integrity of the objects themselves. Because of this,
there is no image degradation as a result of changing any of the objects
attributes. Even
when an object, say a perfect circle, cannot be viewed properly on a monitor
without some distortion, because monitors display in pixels (picture elements),
the circle will exist as a perfect mathematical construct. And, with the right
output device will appear so.
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| Illustrator vector file viewed in outline mode. © 2000 Don Arday. |
Vector graphics are also referred to as “device
resolution independent”, which is sort of an oxymoron. Although a vector
document is dependent on a monitor or a printing device in order to be seen, the
data itself always remains independent of any form of display or output. For
instance, a vector image printed on a high-resolution 9600dpi printer will have
a resolution of 9600dpi, and the same file printed on a low-resolution 300dpi
printer, will have 300 as its resolution, and so on, but the original document
data does not change.
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| Illustrator vector file viewed in preview mode. © 2000 Don Arday. |
Vector files are much smaller than raster ones due to vector documents
being based only on mathematical descriptions and not on pixels. For this
reason vector files are extremely portable and very well suited to certain
functions. Resizing a vector image is done by multiplying the mathematical
description of the objects in the image by a scaling factor, so a file size of
a vector illustrations will be the same whether it is output
as a 3”
x 4” spot illustration or it has been resized to be output as a 12’ x 16’ mural.
Strengths
Small, efficient file sizes.
Infinite scalability of images without a loss of quality.
Excellent type rendering, manipulating, and editing
abilities.
Ability to apply mathematical operations to image
components.
Accuracy in rendering geometric forms.
Ability to edit image elements.
Weaknesses
Ability to render continuous tone full color images.
Ability to globally edit color brightness, contrast, hue, saturation and
value.
Ability to apply editing filters to images.
Raster
Raster software is pixel oriented. Raster files are made
up of individual picture elements, or pixels that are perfectly aligned arrays
of color and value. Pixels run edge to edge, covering the entire surface of the
image. Straight and curved lines, and shapes are all combinations of pixels.
The size, position and attributes of parts of an image are all relative to
their makeup in pixels. The
resolution or size of a raster illustration relates to, and is limited by, the
number of pixels contained within it. As a side note, raster images display
truly on monitors because both raster images and monitor displays are made of
pixels, whereas monitors simulate vector images, which have no pixels.
Raster images are “device resolution dependent”. The output quality of an illustration is dependent
upon the resolution required by the display or output device. This
means that illustrators must know the
intended function for their illustration in order to properly create it. For
instance, a 3” x 4” Photoshop illustration for use on the web can be created at
72ppi (pixels per inch), and it would display smoothly, but the same file
printed on a 1200dpi image setter would look jagged and “pixilated”. In other
words, the pixels that make up the illustration would be conspicuous to the
viewer making the image quality appear very poor. Conversely, that same 3” x 4”
illustration created at 300ppi would print nicely, but used on the web, it
would slow down or pause the loading of a webpage. Due to device resolution
dependence images are not upwardly scalable. (See Digital Image Resolution a prior post for more information on
scaling.)
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| Photoshop raster version enhanced by raster image operation editing. © 2000 Don Arday. |
Raster files are much larger than vector files. This is because all the
attributes, including the location and color of every single, individual pixel
must be recorded, not to mention any saved operations or specialized layer
data. All this can result in massive file sizes for raster illustrations;
especially those that are created for high-resolution output devices.
Strengths
Ability to render continuous tone full color images.
Ability to globally edit color brightness, contrast, hue, saturation and
value.
Ability to apply editing filters to images.
Weaknesses
Large file sizes.
Poor scalability of files.
Poor ability to render, manipulate, and output type.
Poor ability to generate geometric forms.
